1. Field of the Invention
The invention relates to a method and apparatus for fluid handling. More specifically, the invention relates to a method and apparatus for controlling fluid flow via pressure regulation.
2. Description of the Related Art
Electro-pneumatic control valves are commonly employed to monitor and control pressure output of mechanical booster regulators. The regulators, in turn, operate pneumatic equipment such as welding guns. In the prior art, these control valves generally include a pair of solenoid operated popper valves which open and close in response to the signals from control circuitry to maintain a predetermined pilot pressure as dictated by command voltages selected by the operator. An electro-pneumatic transducer in a feedback loop is generally employed to control the pilot pressure output of the control valves.
Control valves known in the prior art and commercially available today are able to produce very precise pilot pressure, approximately 0.2 PSI of the command pressure. While the pilot pressure of the prior art control valves are precisely monitored, problems exist with the control of the pressure output from the mechanical regulators. Despite the precision of the control valves, the regulators can drift up to 5 psi from their target pressure. These conditions of such extreme drift are unacceptable with todays quality control standards.
To combat this problems, a feedback loop has been employed wherein a transducer is used to monitor the output of the regulator. However, this additional feedback causes other problems. First, with this configuration, the control valve and its control circuitry must include parameters which account for the dynamics of both the solenoid operated valves and the valve in pressure of the mechanical regulator. Typically, the regulator output pressure either over or undershoots the target pressure which causes the control valve to "hunt" for its target. The solenoid operated valves thus open and close in rapid succession causing undue wear, premature failure, pressure instability and emit a noise commonly referred to as "motorboating." Additional feedback lines and additional transducers are typically used to correct this problem. However, they are expensive and can impermissibly raise the cost of the control valves to the point when they become uncompetitive. A description of a variation of a feedback system including two feedback lines is found in applicant's co-pending application Ser. No. 08/371,766, filed Jan. 12, 1995.